Is it when another creature dons the control amulet?
Does the original owner have to expire first?
Is control transferred even if the control amulet is stolen from the previous owner?
The exact scenario is the party has encountered a goblin with a Shield Guardian. They used 'Command' on the goblin and made it 'give' the amulet to them. Does control of the Guardian switch to the player immediately when they don the amulet?